H.264/MPEG-4 Part 10 or AVC (Advanced Video Coding) is a standard for video compression, and is currently one of the most commonly used formats for the recording, compression, and distribution of high definition video. H.264/MPEG-4 AVC is a block-oriented motion-compensation-based codec standard developed by the ITU-T Video Coding Experts Group (VCEG) together with the International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC) joint working group, the Moving Picture Experts Group (MPEG). The product of this partnership effort is known as the Joint Video Team (JVT). The ITU-T H.264 standard and the ISO/IEC MPEG-4 AVC standard are jointly maintained so that they have identical technical content.
H.264 is perhaps best known as being one of the codec standards for Blu-ray Discs; all Blu-ray Disc players must be able to decode H.264. It is also widely used by streaming internet sources, such as videos from Vimeo, YouTube, and the iTunes Store, web software such as the Adobe Flash Player and Microsoft Silverlight, and also various HDTV broadcasts over terrestrial (ATSC, ISDB-T, DVB-T or DVB-T2), cable (DVB-C) and satellite (DVB-S and DVB-S2).
Specified in Annex G of H.264/AVC, SVC allows the construction of bitstreams that contain sub-bitstreams that also conform to the standard, including one such bitstream known as the “base layer” that can be decoded by a H.264/AVC codec that does not support SVC. Temporal bitstream scalability includes the presence of a sub-bitstream with a smaller temporal sampling rate than the main bitstream, while spatial and quality bitstream scalability includes the presence of a sub-bitstream with lower spatial resolution/quality than the main bitstream.
Analog video transmissions degrade gracefully and allow for a lower quality video to be displayed based on signal-to-noise ratio (SNR) and receiver performance. However, digital video transmissions suffer from the brick wall effect of other digital transmissions. Multicast video transmissions typically try to transmit for the least common denominator, which might not be the majority of users and degrade video beyond what the majority of users can receive.
Current approaches include single transmission of the most robust stream which causes degradation for all users. Multiple transmissions would typically use excess bandwidth. A parallel tone modem may fix pilots to certain modulation types but it may suffer from high peak-to-average power ratio (“PAPR”), and is susceptible to frequency selective fading. Also, unequal coding such that more significant bits are encoded stronger than less significant bits may require a new modulation scheme requiring a significant modem change, and for a single H.264 stream, no single bit is more important than the rest due to excessive compression.